When the critical day, 27 May 1782, arrived on which parliament met to receive the decision of the ministry touching its claim to legislative independence, the duty of guarding the approaches to the house was assigned to Tandy and his corps of artillery. He played an equally conspicuous part on 10 Nov. 1783 when the volunteer convention, with the bishop of Derry as the most prominent figure, proceeded through the streets of Dublin to the Rotunda for the purpose of discussing, and it was hoped of settling, the question of parliamentary reform.
That day saw Tandy at the height of his fame. With the decline of the volunteer movement his influence began to wane. Being charged in parliament by the attorney-general, John Fitzgibbon (afterwards Earl of Clare), with having fomented the riots that took place in Dublin at the beginning of the Duke of Rutland’s administration in 1784, Tandy denied the allegation in a public advertisement couched in the most offensive language. Fitzgibbon, who regarded him with undisguised contempt, took no notice of his abuse, and merely kept out of his way when Tandy, in order to fasten a quarrel on him, paraded the lobby of the house with a sword significantly displayed at his side.